The present invention relates to an actuator which is used for transferring a head of a magnetic disk drive and the like.
Hereinafter, a conventional actuator will be described with reference to FIGS. 7 to 10.
FIGS. 7 to 10 are diagrams for illustrating structures of a conventional actuator. FIG. 7 is a sectional view illustrating the actuator. FIG. 8 is a perspective view illustrating a moving part of the actuator. FIG. 9 is a sectional view illustrating a metallic mold for forming the moving part of the actuator. And, FIG. 10 is an enlarged view illustrating a terminal section of FIG. 9.
In FIG. 7, numerals 21a and 21b denote opposite yokes which are provided with a predetermined space therebetween; numeral 22 denotes a coil which is movably wound between the yokes 21a and 21b; and numeral 23 denotes a permanent magnet which is attached between the yokes 21a and 21b, and to at least one of the yokes, and applies a magnetic field to the coil 22. The permanent magnet 23 is attached to the yoke 21a in the example shown in FIG. 7, magnetized as shown in this figure, and applies a magnetic flux to the coil 22.
In FIG. 8, numeral 22 denotes the coil which is movably wound between the yokes 21a and 21b, and numeral 25 denotes a holding member made of a thermoplastic resin, which holds the coil 22. Numeral 26 denotes a housing made of metal material such as aluminum alloy and the like. A rotation constraint mechanism can be fitted in a hole 27 provided in the housing 26, and a magnetic head can be fitted in a hole 28 (the rotation constraint mechanism and the magnetic head are not shown in this figure). Numerals 29a and 29b denote terminals to which both end parts of a strand of the coil 22 are electrically connected. Usually, the terminals 29a and 29b are inexpensive, so pin-shaped ones made of conductive material are employed. Numeral 30 denotes a flexible circuit board including a conductor part which transmits a current from a current generation source (not shown) to the coil 22 via the pin-shaped terminals 29a and 29b. 
In FIG. 8, the coil 22 is wound in a shape of a trapezoid, and when a current in a clockwise direction is passed through the coil 22, a force is generated in the coil 22 in accordance with Fleming""s left hand rule, and the coil 22 moves in a direction of arrow 24. In this case, in FIG. 7, in a part on a right side of the coil 22, a current flows from a far side to a near side, and in a part on a left side of the coil 22, the current flows from a near side to a far side. When a current in a counterclockwise direction is passed through the coil 22, the coil 22 moves in an opposite direction to that of arrow 24. In this case, in FIG. 7, in a part on the right side of the coil 22, a current flows from a near side to a far side, and in a part on the left side of the coil 22, a current flows from a far side to a near side. Here, the coil 22 is set by a stopper (not shown) to move only within a coil movable range.
Next, a production method of the conventional movable part will be described with reference to FIGS. 8 and 9.
In FIG. 9, numerals 31a and 31b denote metallic molds and, for convenience sake, the metallic mold 31b is described as an upper part, but the mold 31b is a lower mold and the mold 31a is an upper mold. Numeral 32 denotes a direction of separation between the metallic molds 31a and 31b. 
Initially, coil 22, pin-shaped terminals 29a and 29b (not shown in FIG. 9) to which the coil 22 is connected, and housing 26 are positioned in the metallic molds 31a and 31b, and thermoplastic resin is injected into the metallic molds 31a and 31b, thereby forming holding member 25, and integrating the coil 22, the housing 26, and the pin-shaped terminals 29a and 29b. In FIG. 9, in the metallic molds 31a and 31b, a longitudinal direction of the pin-shaped terminals 29a and 29b is directed in the same direction as the separation direction 32.
Next, flexible circuit board 30 is fixed on the housing 26 by a fastening device such as a screw (not shown). At this time, parts of the pin-shaped terminals 29a and 29b, exposed from the holding member 25, are inserted into holes 30a and 30b provided in a conductor end part of the flexible circuit board 30, and projecting parts of the pin-shaped terminals 29a and 29b and the conductor part are connected electrically with solder.
Next, a structure of a pin-shaped terminal section in the conventional movable part will be described with reference to FIG. 10.
In this figure, one end of the pin-shaped terminal 29a is held by the holding member 25, and another end is exposed from the holding member 25. Coil strand 22c is wound on a part of the pin-shaped terminals 29a, which is buried in the holding member 25, and electrically connected thereto with solder 33a. Further, in a state where the exposed part of the pin-shaped terminal 29a is inserted into the hole 30a provided in the flexible circuit board 30, the exposed part and the conductor part 30c of the flexible circuit board 30 are electrically connected with solder 33b. In addition, the pin-shaped terminal 29b is similarly connected to the coil 22 and the flexible circuit board 30.
According to the above-mentioned construction, the coil is of a flat type and therefore the separation direction 32 is set to be perpendicular to a coil moving direction, for convenience during production in the metallic molds. In addition, it is difficult to arrange a longitudinal direction of the pin-shaped terminals parallel with the coil moving direction, for convenience during production in the metallic molds, and therefore the longitudinal direction of the pin-shaped terminal is directed in the same direction as the separating direction 32.
Therefore, in order to ensure a length of the pin-shaped terminals, which is required for positioning in the metallic mold, a prescribed length is required. Further, because the pin-shaped terminals exposed from the holding member are inserted into the holes in the conductor end part of the flexible circuit board and electrically connected by solder, the exposed parts of the pin-shaped terminals cannot be shortened. In addition, the part of the pin-shaped terminal, which is buried in the holding member, cannot be shortened because the part is wound by the coil strand and electrically connected thereto with the solder.
The longitudinal direction of the pin-shaped terminal formed as described above corresponds to a thickness direction of an apparatus into which the actuator is installed, and in such construction, while thinner apparatus are demanded in recent years, it is very difficult to provide these thinner apparatus.
In addition, as described above, in a state where pin-shaped terminals are inserted into the holes provided in the flexible circuit board, the pin-shaped terminals are covered and connected by solder, and therefore pin-shaped terminal connecting parts on the flexible circuit board become larger. As a result, adjacent permanent magnets or yokes become smaller, which prevents an actuator in its entirety from generating a large torque.
Further, since two pin-shaped terminals have the same shape, when these terminals are positioned in metallic molds, they may be erroneously placed. Accordingly, a direction of current which passes through the coil becomes opposite to a proper direction, which causes a malfunction in that the movable part of the actuator moves in an opposite direction.
The present invention is made to solve the above-described problems, and has for its object to provide an actuator which can thin an apparatus into which the actuator is installed and prevent resultant malfunction.
The present invention is made to achieve the above-mentioned object, and in accordance with a first aspect of the invention an actuator comprises: plural yokes which confront each other while providing a predetermined space therebetween; a coil which is wound and movably placed between the plural yokes; a permanent magnet which is located between the plural yokes and attached to at least one of the yokes, and which applies a magnetic field to the coil; a holding member for holding the coil, which holding member is made of a thermoplastic resin; a housing to which the holding member is attached at one end, and to which a functional member can be attached at another end; and a flexible circuit board which transmits a current from an exterior to the coil, wherein portions of two plate-shaped terminals to which opposite end parts of a strand of the coil are electrically connected are buried in the holding member and exposed parts of both plate-shaped terminals are electrically connected to a conductor part of the flexible circuit board.
According to a second aspect of the present invention, in the actuator of the first aspect, the two plate-shaped terminals are buried in a side part of the holding member so that longitudinal directions of the terminals are parallel with a coil movable direction.
According to a third aspect of the present invention, in the actuator of the first aspect, the two plate-shaped terminals are buried in a side part of the holding member so that longitudinal directions of the terminals are parallel with a coil movable direction, and both plate-shaped terminals are provided on a flat surface.
According to a fourth aspect of the present invention, in the actuator of the first aspect, the two plate-shaped terminals are formed by integrally burying two plate-shaped terminals in the holding member, which is made of the thermoplastic resin, via a molding operation, and thereafter separating exposed parts of this integral structure into two pieces.
According to a fifth aspect of the present invention, in the actuator of the first aspect, end parts of the two plate-shaped terminals, which end parts are connected to the coil strand, have different shapes, respectively.
According to a sixth aspect of the present invention, in the actuator of the fifth aspect, one of the end parts of the two plate-shaped terminals, which end parts are connected to the coil strand, is longer than the other.
According to a seventh aspect of the present invention, in the actuator of the fifth aspect, one of the end parts of the two plate-shaped terminals, which end parts are connected to the coil strand, is crank-shaped.
As described above, an actuator according to the first aspect of the present invention comprises: plural yokes which confront each other while providing a predetermined space therebetween; a coil which is wound and movably placed between the plural yokes; a permanent magnet which is located between the plural yokes and attached to at least one of the yokes, and applies a magnetic field to the coil; a holding member for holding the coil, which holding member is made of a thermoplastic resin; a housing to which the holding member is attached at one end, and to which a functional member can be attached at another end; and a flexible circuit board which transmits a current from an exterior to the coil, wherein portions of two plate-shaped terminals to which opposite end parts of a strand of the coil are electrically connected are buried in the holding member, and exposed parts of both plate-shaped terminals are electrically connected to a conductor part of the flexible circuit board. Therefore, both plate-shaped terminals can be placed at arbitrary positions in the holding member, and a movable part of an actuator which consists of the coil, the holding member, the housing, the plate-shaped terminals and the flexible circuit board can be thinner, and consequently, an apparatus into which the actuator of the present invention is installed can be thinner.
According to the second aspect of the present invention, in the actuator as defined in the first aspect, the two plate-shaped terminals are buried in a side part of the holding member so that longitudinal directions of the terminals are parallel with a coil movable direction. Therefore, a movable part of the actuator which consists of the coil, the holding member, the housing, the plate-shaped terminals and the flexible circuit board can be thinner, and consequently an apparatus into which the actuator of the present invention is installed can be thinner.
According to the third aspect of the present invention, in the actuator as defined in the first aspect, the two plate-shaped terminals are buried in a side part of the holding member so that longitudinal directions of the terminals are parallel with a coil movable direction, and both plate-shaped terminals are provided on a flat surface. Therefore, connecting parts of both plate-shaped terminals and the flexible circuit board can be smaller, and a movable part of the actuator which consists of the coil, the holding member, the housing, the plate-shaped terminals and the flexible circuit board can be thinner, and consequently, an apparatus into which the actuator of the present invention is installed can be thinner. Further, due to miniaturization of the connecting parts of the plate-shaped terminals and the flexible circuit board, adjacent yokes or permanent magnets can be enlarged, whereby a large torque can be obtained.
According to the fourth aspect of the present invention, in the actuator as defined in the first aspect, the two plate-shaped terminals are formed by burying portions of two integrally constructed plate-shaped terminals in a holding member which is made by molding thermoplastic resin, and thereafter separating exposed parts of the plate-shaped terminals into two pieces. Therefore, both plate-shaped terminals can be easily formed on the flat surface, and a movable part of the actuator which consists of the coil, the holding member, the housing, the plate-shaped terminals and the flexible circuit board, and consequently an apparatus into which the actuator of the present invention is installed, can be thinner. Further, when molded in metallic molds, the integrated two plate-shaped terminals are employed, and therefore handling of the terminals becomes easier than that of the prior art.
According to the fifth aspect of the present invention, in the actuator as defined in the first aspect, end parts of the two plate-shaped terminals, which end parts are connected to the coil strand, have different shapes, respectively. Therefore, discrimination between the two plate-shaped terminals is easier and an assembly failure of erroneously connecting the terminals and the coil strand can be prevented. In addition, when molded in metallic molds, an erroneous placement of the plate-shaped terminals in the metallic molds is prevented and both plate-shaped terminals can be correctly connected at predetermined positions of the flexible circuit board, whereby a malfunction of the coil moving in an opposite direction can be prevented.
According to the sixth aspect of the present invention, in the actuator as defined in the fifth aspect, one of the end parts of the two plate-shaped terminals, which end parts are connected to the coil strand, is longer than the other. Therefore, discrimination between both plate-shaped terminals is easier, and an assembly failure of erroneously connecting the terminals and the coil strand can be prevented. In addition, when molded in the metallic molds, an erroneous placement of the plate-shaped terminals in the metallic molds is prevented and both plate-shaped terminals can be correctly connected at predetermined positions of the flexible circuit board, whereby a malfunction of the coil moving in an opposite direction can be prevented.
According to the seventh aspect of the present invention, in the actuator as defined in the fifth aspect, one of the end parts of the two plate-shaped terminals, which end parts are connected to the coil strand, is crank-shaped. Therefore, discrimination between both plate-shaped terminals is easier, and an assembly failure of erroneously connecting the terminals and the coil strand can be prevented. In addition, when molded in the metallic molds, an erroneous placement of the plate-shaped terminal in the metallic molds is prevented and both plate-shaped terminals can be correctly connected at predetermined positions of the flexible circuit board, and a malfunction of the coil moving in an opposite direction can be prevented.